Wire line method and apparatus for cleaning well perforations

ABSTRACT

Sand control operations in cased and perforated wells equipped with a tubing string such as a production tubing string, are improved by first cleaning the perforations by lowering a tool comprising a chamber of fixed volume, an actuator for rapidly opening the chamber, and a means for packing off the tubing string above the production interval into the well on a wire line; packing off the interval adjacent the perforations; and rapidly opening the chamber into fluid communication with fluids in the wellbore to surge fluid from the surrounding earth formation through the perforations and into the well.

Uited States Patent 1 Olivier [54] WIRE LINE METHOD AND APPARATUS FOR CLEANING WELL PERFORATIONS [75] Inventor: Donald A. Olivier, Kenner, La.

[73] Assignee: Shell Oil Company, Houston, Tex.

[22] Filed: Oct. 1, 1971 [21] Appl. No.: 185,614

[4 1 Jan. 23, 1973 Primary Examiner-David H. Brown Attorney-Harold L. Denkler et a1.

[5 7] ABSTRACT Sand control operations in cased and perforated wells equipped with a tubing string such as a production tubing string, are improved by first cleaning the perforations by lowering a tool comprising a chamber of fixed volume, an actuator for rapidly opening the chamber, and a means for packing off the tubing string above the production interval into the well on a wire line; packing off the interval adjacent the perforations; and rapidly opening the chamber into fluid communication with fluids in the wellbore to surge fluid from the surrounding earth formation through the perforations and into the well.

11 Claims, 4 Drawing Figures PATENTEU JAN 23 197-3 SHEET 1 UF 3 CURRENT SOURCE FIG. 1

PAIENTED JAN 23 I975 SHEET 2 BF 3 PMENIEDJAN 23 I975 SHEET 3 [IF 3 FIG/4 WIRE LINE METHOD AND APPARATUS FOR CLEANING WELL PERFORATIONS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to the field of completing wells and more particularly, to method and apparatus for cleaning perforations in a cased and perforated well prior to installation of sand control means.

2. Description of the Prior Art In completing wells, such as oil wells, it is common practice to drill the well bore hole into an oil containing formation, cement a tubular casing throughout the length of the bore hole, and thereafter perforate the casing and cement adjacent the oil containing formation to open the formation into fluid communication with the interior of the casing. If the oil containing formation behind the perforated casing is unconsolidated, it may be necessary to provide means for excluding sand from the well bore if the well is to be operated efficiently.

It has been found that the presence of unconsolidated sand even in small quantities can seriously effect the operation of both producing and injection wells. Besides high rate of wear on subsurface and surface equipment due to sand abrasion, partial or complete plugging of a well can occur. If no sand control means is provided, expensive well cleanout is frequently required. In extreme instances the cleanout may not be possible and the well must be abandoned.

Two widely used sand exclusion methods are the installation of gravel or sand packs in the well bore adjacent the productive interval and the consolidation of the formation sand in and/or around the well bore. Consolidation may, for example, be achieved by injecting plastics are resins into the formation or by metal plating the formation. Such consolidation techniques are, for example, described in U.S. Pat. Nos. 3,294,166 and 3,393,737.

In some oil producing regions where unconsolidated sands are common and where the above-mentioned sand control methods are frequently used, a high incidence of sand control failure with associated casing damage has been observed. An important factor causing this failure is injectivity impairment into the unconsolidated sands adjacent the perforated interval of the well bore. It is believed that injectivity impairment may be caused by a number of factors. Among these are pul varized material from the cement sheath, pulvarized and compacted formation material, and perforation charge debris. When using sand consolidating techniques to control sand, the impairment can prevent injection of consolidating fluids into the formation through some of the perforations. This prevents complete consolidation of the interval adjacent the well bore. Additionally, treatment of impaired perforations can cause the impairment to become locked in place by the consolidating material.

It has also been found that permeability impairment in unconsolidated sands can inhibit deposition of gravel in perforation tunnels where sand control is by gravel packing. Tunnels are best filled with gravel if fluid flows out of the well bore through the perforation tunnels thus carrying packing material into these tunnels. The absence of gravel in perforation tunnels allows fine formation sand to fill in the tunnels when the well is placed on production. This fine formation sand severly restricts fluid flow, and thereby decreases well productivity.

A number of techniques have been proposed for improving injectivity into the unconsolidated interval prior to the installation of sand control means. Among these techniques are acid stimulation and fracturing. It has been found that each of these methods has the disadvantage that in many cases acid or fracturing fluid moves into the formation through only some of the perforations. Since all perforations are not opened, uniform placement of sand control means throughout the interval is not assured.

It is known that flow impairing materials can be removed form perforations which extend into consolidated formations by perforating the well with the pressure in the unperforated well casing lower than the formation pressure. This causes formations fluids to surface into the casing carrying debris from the formation. The method is referred to as underbalanced perforating. A second technique which has been successfully used in consolidated formations is to backflow material into the well bore after the well if perforated by reducing well bore pressure. This can be done by swabbing fluid from the well bore to reduce the fluid column in the well.

A major disadvantage of these methods is that it is very difficult to control the amount of fluid which flows into the well bore. If the well bore fluid column is drawn down too much, then an excessively large volume of fluid may surge into the well carrying a large volume of formation sand. When this occurs, it is necessary to remove the sand before sand control means are installed. This, of course, results in additional expenditures of time and increases the cost of sand control installation. Additionally, if an excessively large volume of fluid flows into the well bore, formation sand around the entire casing can be disturbed. This may result in impairment of formation permeability adjacent the well, thus reducing well productivity.

A copending application (P-9609) Ser. No. 163,856, filed July 19, 1971, teaches the well perforations can be cleaned of perforation debris without sanding up the well bore and without creating permeability impairment of the adjacent formation by disturbing sands adjacent well bore by a method which comprises the steps of packing off the perforated interval of the well with at least one packer to isolate the perforated zone from the rest of the well; positioning adjacent the packed off interval a chamber of a selected volume containing a gas at a pressure substantially lower than the formation pressure; and rapidly opening the chamber into fluid communication with the packed-off perforated interval whereby a selected volume of fluid surges from the fluid containing formation, through the perforations and into the well carrying debris from the perforations into the well. The debris may be permitted to settle to the bottom of the well prior to the installation of sand exclusion means.

The method of the above-mentioned copending application contrasts with the operation of a number of prior art tools employing implosive reactions to clean well perforations, for example the tools described in U.S. Pat. Nos. 2,361,558; 3,209,834; and 3,255,820. These prior art tools, instead of flowing a selected volume of fluid into the well through the perforations to carry debris into the well, generate a brief initial decrease in pressure in a well bore followed by a surge of increased pressure. This positive pressure surge drives fluid outwardly from the wellbore through the well perforations and into the surrounding earth formation. The outwardly surging fluid cleans the perforations and, in some cases, fractures the adjacent earth formation.

If such tools are used to clean perforations prior to the placement of sand exclusion means, debris may be forced back into the formation adjacent the perforations by the outwardly surging fluid. This debris may be locked in by the subsequently placed sand exclusion means and there-after impair fluid flow into the well bore.

Copending application Ser. No. 163,856 (P-9609) teaches that the chamber of lower pressure is preferably provided by disposing upper and lower valve means in a string of tubular pipe thereby forming a chamber-portion within the string of pipe between the valve means when they are closed. The chamber is operatively positioned by extending the string of pipe into the well. Opening the lower valve opens the chamber into fluid communication with the packed-off interval.

In some cases it is desired to install in situ sand consolidation means in a well which is already provided with production equipment including a production tubing string. For example, the need for such sand exclusion means may not be determined until the well has been produced for some time, or it may be necessary to treat a well in which a previously installed sand exclusion means has failed, or it may be desired to install sand exclusion means in an old well which is recompleted using a concentric tubing technique in which a string of tubing is cemented within the original casing string, perforated, and thereafter used as a flow conduit to produce oil from the re-completed zone. In such cases the cost of cleaning perforations according to the teachings of copending application (P-9609) Ser. No. 163,856 can be significantly reduced if a tool is available which is capable of being lowered into the well to be treated through the in place tubing string on a wire line. This will eliminate any need to move the existing tubing string or to lower a third, even smaller diameter, tubing into the well bore.

SUMMARY OF THE INVENTION It has now been discovered that in wells in which production tubing strings have been previously installed, well perforations which open the well into fluid communication with an unconsolidated, fluid containing subsurface earth formation can be cleaned of perforation debris without moving the existing well tubing by a method which comprises the steps of lowering a chamber of a selected volume containing a gas at a pressure substantially lower than the formation pressure along with a packoff means into the well on a wire line through the tubing string; packing off the tubing string near the lower end thereof and above the chamber to isolate the perforated zone from any fluids in the tubing above the packoff; rapidly opening the chamber into fluid communication with the packed off portion of the tubing whereby fluid surges from the fluid containing formation through the perforations into the well carrying debris from the perforations into the well; and allowing debris to settle to the bottom of the well.

Apparatus for practicing the method of this invention comprises a flow tool comprising a housing including a hollow, elongate close-walled chamber portion and a port section having at least one opening or port for fluid flow in the housing wall, frangible plug means sealingly positioned in the housing between the chamber portion and the port section for preventing fluid communication between the chamber portion and the port section, and means for breaking the frangible plug means. The latter means preferably comprises a firing chamber, a piston slidably mounted in the firing chamber, frangible disc shattering means operatively connected to the piston and explosive igniting means connected to the firing chamber. When the firing chamber is loaded with an explosive, ignition of the explosive by the explosive igniting means creates an expanding gas which rapidly moves the piston in the firing chamber causing the frangible disc shattering means to shatter the frangible disc thereby opening the chamber to fluid flow. The apparatus also comprises coupling means for connecting the flow tool to a wire line and means for packing off the tubing above the flow tool when the latter is positioned for operation.

In a preferred embodiment the means for packing off the tubing comprises seating nipple means disposed in the tubing string and hollow pack-off means for sealingly engaging the seating nipple releaseably connected to the wire line. The pack-off means advantageously has a bore therethrough through which the wire line passes, and throat means for sealingly engaging the housing of the flow tool to close the bore of the pack-off means to fluid flow.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1 we see a portion of a well 10 which extends from the earth surface (not shown) to a fluid containing formation 11. The well is completed in a conventional way by cementing a tubular casing 12 through the formation of interest 11 and then perforating the casing 12 with a number of perforations 13 to open the interior of casing into communication with formation 11.

The well 10 is equipped with a production tubing string 14 which extends from the surface to a point near the formation 11. A packer 15 of a conventional type is positioned in the casing 12 above the formation 11 to seal the annular space between the casing 12 and the tubing 14 above the packer 15 from fluid communication with the formation 1 l.-

To clean the perforations 13 prior to the installation of a sand control means, such as an in situ consolidating material, a flow tool 9 comprising a chamber of selected volume 16 (FIG. 2) is lowered into the well through the tubing string 14 on a wire line 17 to a point near the bottom of the tubing 14. The tubing is then packed off above the chamber 16 with a suitable pack off means 18 and the chamber 16 is rapidly opened into fluid communication with the formation 12 by an actuator means 19. (FIG. 2) This allows a selected volume of fluid equal to the volume of the chamber 16 to rapidly move from the formation 11 through the perforations 13 and into the casing 12. This fluid carries plugging debris from perforations 13 into the casing 12. The debris may then be allowed to settle within the well to a point below the perforations 13. The chamber 16 and packoff means 18 can then be withdrawn from the tubing 14 and in situ sand consolidating fluid can be injected down the tubing 14 into the formation 11 to consolidate the unconsolidated formation material.

FIGS. 1 and 2 illustrate a preferred embodiment of an apparatus suitable for the practice of this method. Chamber 16 is preferably formed from a tubular section of one or more lengths of pipe of diameter sufficiently small to pass through the interior of the tubing 14, for example, in 2% OD. tubing, the chamber 16 may comprise 1% OD. tubing. The chamber 16 is closed at its lower end with a plug means such as bull plug 21 and is closed near its upper end with a frangible plug means such as ceramic disc 22. The disc 22 may be held in place by means such as shoulders 23 and 24 in adjacent sections of pipe 25 and 26 which form the upper portion of the wall of the chamber 16. The pipe segments 25 and 26 may be fastened together with any suitable fastening means such as threaded connection 27. A gasket 28 is advantageously positioned between the disc 22 and the shoulder 24 of the pipe segment 26 in order to insure a fluid tight seal. The pipe segment 25 above the disc 22 is provided with a number of fluid inflow passageways or ports 29 through which fluid may flow into the pipe segment 25 from the annulus between the pipe segment 25 and the casing 12.

A frangible disc shattering means such as actuator 19 is connected to pipe segment 25 above the disc 22. A preferred actuator 19 comprises a piston 30 slidably mounted in a cylindrical firing chamber 31 formed in a housing 32. A connecting rod 33 connects the piston 30 to an impact head 34. A piston stop means such as stop ring 35 is positioned at the end of the firing chamber 31 in order to stop the piston after the disc 22 is shattered. The stop ring 35 is affixed to the housing 32 by appropriate fastening means such as set screws 36. A packing gland 37 may be positioned around the connecting rod 33 adjacent the open end of the firing chamber 31 to prevent the flow of fluid into the firing chamber 31. The packing gland may, for example, comprise a metal disc 38 and disc of packing material such as rubber seal 39. Means are provided for compressing the rubber seal 39 against the disc 38 to expand the rubber seal 39 into sealing contact with the connecting rod 33. For example, the set screws 36 may be provided with tapered heads 40 which upon contact with a corresponding locking groove in the stop ring 35 force the stop ring 35 upwardly into sealing contact with the rubber seal 39.

To prepare the actuator 19 for operation, the firing chamber 31 is loaded with an appropriately sized charge of explosive material, such as gun powder 41, which may be held in place by a powder packing material 42 of a suitable type. The piston 30 is then placed in the firing chamber 31 in contact with the packing material 42 and the packing gland 38 and stop ring 35 are then positioned. As the set screws 36 are tightened to fasten the stop ring 35 in place, the rubber seal 39 of the packing gland 37 engages the connecting rod 33 sufficiently tightly to hold the piston 30 in place prior to the firing of the explosive powder 41.

An explosive igniting means such as spark contact 43 is operatively associated with the firing chamber 31. The spark contact 43 is connected with a firing control preferably including a current source at the surface by circuit means such as electrical conduit 44 which may run along the wire line 17 used to lower the apparatus into the tubing 14.

Alternatively, the activator may be provided with an automatic firing means which fires the explosive automatically when the neck 46 of the flow tool 9 seats in the throat 50 of the pack-off means 51. An example of such a mechanism is shown in FIG. 4 and is more fully described below.

The flow tool 9 including actuator 19 and fluid chamber 16 is connected by wire line connector means such as rope socket 45 to a wire line 17 upon which the apparatus may be lowered into he hole. The rope socket 45 advantageously has a neck portion 46 extending upwardly from a circular shoulder part 47. The neck portion 46 is preferably provided with one or more grooves 48 in which sealing means such as rubber 0 rings 49 are positioned to insure a good pack off as the neck is drawn up into the throat section 50 of the zone isolating pack off 51 as hereinafter described.

The flow tool 9 is preferably operated in association with a zone isolating pack-off means 51 of a type adapted to locate in and sealingly engage a seating nipple 52 of a type conventionally used with wire line and pump down tools. The seating nipple 52 conventionally will comprise one or more circumferential, internal locating grooves 5355 and a polished cylindrical bore 56 which may be sealingly engaged by the zone isolating pack off 51. The seating nipple 52 forms a part of the tubing string 14. It must be positioned in the tubing string before that tubing string 14 is run into the well 10. Therefore, the embodiment of the zone isolating pack off 51 described herein is only applicable in those wells in which a seating nipple 52 of the appropriate type has been installed. As stated above, such seating nipples are present in many wells conventionally. Such a nipple is preferably run in any well in which it is expected that the method of this invention may be used.

The zone isolating pack-off means 51 has a hollow bore 57 through which the wire line 17 may freely pass. The body of the pack off carries one or more locating and locking means such as locking keys 58-60 which are adapted to engage the grooves 53-55 and lock the pack-off means 51 in place when these keys are positioned opposite the appropriate grooves of the seating nipple 52. One or more rings of flexible pack-off material such as rubber 0" rings 61 are positioned in grooves in the external wall of the zone isolating packoff means 51 to sealingly engage the polished bore 56 of the seating nipple 52 when the pack-off means 51 is properly positioned in the seating nipple 52. It should, of course, be understood that the special configuration of locking means and pack-off material must be chosen to match the particular seating nipple 52 positioned in the tubing 14.

The lower portion of the pack-off means 51 comprises a cylindrical throat 50 which is adapted to receive the neck 46 of the flow tool 9. The shoulder 47 abuts throat 50 when the neck 46 is drawn into the throat 50. This prevents the neck from becoming wedged in the throat 50. i

The flow tool 9 and zone isolating pack off 51 are preferably run into the well on a combination running-pulling tool 64 of a type which will allow the zone isolating pack off 51 to be positioned in the seating nipple 52, the flow tool 9 to be drawn into the throat 50 of the pack-off means 51, and the entire assembly to be withdrawn from the well 10 all in a single wire line trip. An example of such a running-pulling tool 64 is shown in FIG. 3. In this embodiment the tool 64 comprises an elongated core 65 extending from a base portion 66. The lower end of the core 65 is provided with fastening means such as a threaded connection to which a rope socket 67 may be attached. The rope socket 67 couples the wire line 17 from which the flow tool 9 is suspended to the core 65. The core 65 is also connected to a running neck portion 73 of the pack-off means 51 by releasible connecting means such as tangential shear pins 68 which pass through mounting holes 69 and 70 in the running neck 73 and engage a groove 71 in the core 65. The shear pins 68 may be formed of brass or other suitable shearable material. The wire line 17 is preferably sufficiently long to allow the flow tool 9 to hang at least about 6 inches below the throat 50 of the pack-off means 51 when the core 65 is connected to the running neck 73 of the pack-off means 51. This allows the core 65 to be moved upwardly after the pack off 51 is positioned in the seating nipple 52 in order to shear the shear pins 68. After the pins are sheared, the neck 46 of the flow tool 9 may be drawn into the throat 50 of the pack-off means 51 to complete the isolation of the perforated portion of the casing 12 as shown in FIG. 1.

Also extending downwardly from the base portion 66 of the running-pulling tool 64 are a plurality of flexible arms 74 suitable for lockingly engaging a ridge 75 of a pulling neck 76 which is slidably mounted upon the running neck 73 of the pack-off means 51. As shown in FIG. 1, the pulling neck 76 is coupled to the locking key or dogs 58 of the pack-off means 51. Upwardly motion of the pulling neck 76 slides the locking keys 58 upwardly along the inclined barrel 77 of the pack-off means 51 thereby releasing the locking keys 58 so that the pack-off means 51 may be withdrawn upwardly from the seating nipple 52. In the embodiment shown, the core 65 of the running-pulling tool 64 extends downwardly into the hollow bore 57 of the pack-off means 51 when the arms 74 engage the pulling neck 75.

Advantageously, an impact means such as a jar 78 of a conventional type is connected to the running-pulling tool to improve the efficiency of the running and pulling operation. This jar is connected to a rope socket 79 connected to wire line 80 which extends from running means (not shown) at the surface.

The jars 78 are particularly effectively used in combination with an automatic explosive igniting means of a type capable of causing powder 41 to explode in response to the upward movement of the neck portion 46 of the firing tool 9 into the throat 50 of the zone isolating pack-off .means 51. The automatic firing means may, for example, comprise a means which detonates when impacted, such as detonator cap 81 (FIG. 4), positioned in a firing chamber 82 in an actuator means 83 similar to activator means 19 of FIG. 2. (In FIGS. 2 and 4 like numbers refer to like parts of the flow tool 9.)

An impact means such as firing pin 84 is preferably movably positioned within the actuator means 83 for impacting the detonator cap 81 to actuate the flow tool 9 automatically as the tool 9 is drawn into pack-off 51. For example, the firing pin 84 may be biased toward a position in contact with the detonator cap 81 by means such as spring 85, but held in a cocked position by releaseable restraining means such as shear pins 86. The shear pins 86 are positioned in the flow tool 9 in such a way that they are sheared by upward tension on wire line 17 after neck portion 46 of the tool 9 seats in the throat 50 of flow tool 51. In a preferred embodiment, the actuator 83 may comprise a wire line fastener means 87 attached to the wire line 17 and slideably mounted within a housing 88 which forms a part of the neck 46 of the tool 9. The fastener 87 is advantageously free to move axially upwardly within the housing a distance at least equal to the thickness of the shear pins 86. The fastener 87 is connected to the firing pin 84 by means which include the shear pins 86. For example, the shear pins 86 may releaseably connect the fastener 87 to a hollow cylindrical piston 89 connected to the firing pin 84 and axially moveably positioned in the housing 88. A piston stop means such as a shoulder 90 of housing 88 is positioned to restrict the upward movement of the piston 89 so that the fastener 87 may be drawn upwardly away from the piston 89, shearing the pins 86 and thereby freeing the firing pin to be moved by the spring from a cocked position to a firing position in which the pin contacts the detonator cap 81. A restraining means such as clamp 91 is preferably connected to the wireline 17 adjacent the top of he tool 9 to prevent downward movement of the line 17 into the tool 9, as the tool is lowered into the hole.

The shear pins 86 must be sufficiently strong to support the weight of the flow tool 9. Therefore, it is advantageous to run the tool in the embodiment of FIG. 4 with jars 78, as shown in FIG. 3, to insure that adequate upward force may be applied to the wire line 17 to shear the pins 86.

In operation, the apparatus of this invention is run into the well in the configuration shown in FIG. 2. As the pack-off means 51 passes through the seating nipple 52 the locking keys 59 and 60 will expand to,

prevent further downward movement of the pack-off means 51. At this time, the locking keys 58 will fall into place in the groove 53 and the pack-off means 51 will be firmly positioned in the nipple 52. An upward strain on the line 80 will then shear the pins 68, freeing the running-pulling tool 64 from the pack off 51. Further raising of the line 80 will draw the neck 46 of the flow tool 9 into the .throat 50 of the pack-ofi means 51. Thereafter, an appropriate signal can be sent from the surface to ignite powder 41 to drive piston 30 downward whereupon impact head 34 strikes frangible disc 22 thereby opening the wellbore into fluid communication with the chamber 16.

I claim as my invention 1. Apparatus lowerable into a well on a wire line for cleaning well perforations in a well having a casing perforated adjacent a subsurface earth formation which contains a fluid at a formation pressure comprising:

a flow tool which comprises:

a housing having a hollow, elongate close-walled chamber portion of selected volume containing a gas at a pressure substantially below the formation pressure and a port section which is provided with at least one opening for fluid flow through the housing wall; frangible plug means sealingly positioned in the housing between the chamber portion and the port section for preventing fluid communication between the chamber portion and the port section; and means for breaking the frangible plug means to open the chamber portion of the housing into fluid communication with the port section of the housing; means for connecting the flow tool to a wire line;

and means for packing off the well above the port section of the flow tool when the flow tool is lowered into the well to a point adjacent the perforations to be cleaned, thereby isolating the casing adjacent the perforations to be cleaned from fluids in the well above the pack-off means; whereby, upon breaking of the frangible plug means of the flow tool, fluid flows from the fluid-containing earth formation adjacent the perforations through the perforations and into the casing. 2. The apparatus of claim 1 wherein the frangible plug means comprises a ceramic disc.

3. The apparatus of claim 1 wherein the means for breaking the frangible plug means comprises:

an actuator housing mounted in the housing of the flow tool and having a cylindrical firing chamber therein; a piston slideably mounted in the firing chamber; frangible plug shattering means operatively connected to the piston; and explosive igniting means associated with the firing chamber; whereby, when the firing chamber is loaded with an explosive, ignition of the explosive by the explosive igniting means creates an expanding gas which rapidly moves the piston in the firing chamber and causes the frangible plug shattering means to forcefully contact the frangible plug means thereby shattering the frangible plug means. 4. The apparatus of claim 3 wherein the explosive igniting means comprises:

electrical spark means positioned in the firing chamber; electrical current generating means at the earth surface; and circuit means operatively connecting the electrical current generating means with the electrical spark means.

5. The apparatus of claim 3 wherein the explosive igniting means comprises:

detonator means which explodes upon impace positioned in the firing chamber; 5 a firing pin slideably positioned in the actuator housing for impacting the detonator means;

biasing means for driving the firing pin into contact with the detonator; and

restraining means releaseably connected to the firing pin for holding the firing pin in a cocked position not in contact with the detonator.

6. The apparatus of claim 1 wherein the means for packing off the well above the flow tool comprises:

a string of tubular pipe of smaller diameter than the casing, extending into the well through the casing to a point adjacent the subsurface earth formation;

means for sealing the annular space between the string of tubular pipe of smaller diameter and the casing to fluid flow positioned in the casing above the subsurface earth formation; and

means for packing off the interior of the string of tubular pipe of smaller diameter connected to the wire line above the flow tool.

7. The apparatus of claim 6 wherein the means for packing off the interior of the string of tubular pipe of smaller diameter comprises a zone isolating pack-off means which includes a hollow body portion having a through-bore through which the wire line may pass, locking means connected to the body portion for fixedly positioning the zone isolating pack-off means in the string of tubular pipe of smaller diameter, sealing means connected to the body portion for sealingly engaging the interior wall of the string of tubular pipe of smaller diameter, and a hollow throat section connected to the lower end of the body portion;

wherein the upper portion of the housing of the flow tool comprises a neck having sealing means thereon whereby the neck may be drawn into sealing engagement with he throat section of the zone isolating pack-off means; and including means for releaseably connecting the zone isolating pack-off means to the wire line above the flow tool in spaced relationship with the flow tool; whereby tool, while in spaced relationship, may be run into the well through the tubular pipe of smaller diameter to a point adjacent the subsurface earth formation at which point the locking means fixedly position the zone isolating pack-off means in the string of tubular pipe of smaller diameter, and whereby the zone isolating pack-off means may then be disconnected from the wire line thereby allowing the neck of the flow tool to be raised into sealing engagement with the throat section of the zone isolating pack-off means to pack off the interior of the string of tubular pipe of smaller diameter above the port section of the flow tool prior to cleaning the perforations.

8. The apparatus of claim 7 including a seating nipple having a polished bore and one or more circular-internal grooves for receiving the locking means of the zone isolating pack-off means, the seating nipple being positioned in the string of tubular pipe of smaller diameter at a point adjacent the subsurface earth formation at which it is desired to pack off the interior of the string of tubular pipe of smaller diameter.

the zone isolating pack-off means and the flow I 9. The apparatus of claim 7 including means for reconnecting the zone isolating pack-off means to the wire line after cleaning the perforations.

10. The apparatus of claim 9 wherein the means for releaseably connecting the zone isolating pack-off means to the wire line comprises at least one shear pin and wherein the means for reconnecting the zone isolating pack-off means to the wire line comprises at least two flexible arms operatively connected to the wire line and having upset ridges near the lower end thereof for lockingly engaging the zone isolating packoff means.

11. In a method of cleaning well perforations, in a well having a casing perforated adjacent a subsurface earth formation containing a fluid at a formation pressure, of the type wherein the perforated interval of the well bore is packed off with at least one packer to isolate the perforated interval of the well from fluids in the well above the perforated interval, and wherein a chamber of selected volume containing a gas at a pressure substantially lower than the formation pressure is then rapidly opened into fluid communication with the packed-off perforated interval to cause a selected volume of fluid to surge from the formation through the perforations into the casing carrying debris from the perforations into the well; the improvement which comprises, in a well having a relatively small diameter tubing extending into the casing to a point adjacent the perforated interval, the space between the casing and the tubing being closed above the perforated interval to fluid flow from the formation, the steps of:

affixing to a wire line a flow tool comprising a chamber of selected volume closed at one end with a frangible disc and comprising a means for breaking the frangible disc; affixing to the wire line, above the flow tool, a means for packing off the tubing; lowering the flow tool and pack-off means into the tubing to a point adjacent the perforated interval of the casing; packing off the tubing; activating the means for breaking the frangible disc to open the chamber into fluid communication with the perforated interval of the casing; and withdrawing the low tool and pack-off means from the well. 

1. Apparatus lowerable into a well on a wire line for cleaning well perforations in a well having a casing perforated adjacent a subsurface earth formation which contains a fluid at a formation pressure comprising: a flow tool which comprises: a housing having a hollow, elongate close-walled chamber portion of selected volume containing a gas at a pressure substantially below the formation pressure and a port section which is provided with at least one opening for fluid flow through the housing wall; frangible plug means sealingly positioned in the housing between the chamber portion and the port section for preventing fluid communication between the chamber portion and the port section; and means for breaking the frangible plug means to open the chamber portion of the housing into fluid communication with the port section of the housing; means for connecting the flow tool to a wire line; and means for packing off the well above the port section of the flow tool when the flow tool is lowered into the well to a point adjacent the perforations to be cleaned, thereby isolating the casing adjacent the perforations to be cleaned from fluids in the well above the pack-off means; whereby, upon breaking of the frangible plug means of the flow tool, fluid flows from the fluid-containing earth formation adjacent the perforations through the perforations and into the casing.
 2. The apparatus of claim 1 wherein the frangible plug means comprises a ceramic disc.
 3. The apparatus of claim 1 wherein the means for breaking the frangible plug means comprises: an actuator housing mounted in the housing of the flow tool and having a cylindrical firing chamber therein; a piston slideably mounted in the firing chamber; frangible plug shattering means operatively connected to the piston; and explosive igniting means associated with the firing chamber; whereby, when the firing chamber is loaded with an explosive, ignition of the explosive by the explosive igniting means creates an expanding gas which rapidly moves the piston in the firing chamber and causes the frangible plug shattering means to forcefully contact the frangible plug means thereby shattering the frangible plug means.
 4. The apparatus of claim 3 wherein the explosive igniting means comprises: electrical spark means positioned in the firing chamber; electrical current generating means at the earth surface; and circuit means operatively connecting the electrical current generating means with the electrical spark means.
 5. The apparatus of claim 3 wherein the explosive igniting means comprises: detonator means which explodes upon impace positioned in the firing chamber; a firing pin slideably positioned in the actuator housing for impacting the detonator means; biasing means for driving the firing pin into contact with the detonator; and restraining means releaseably connected to the firing pin for holding the firing pin in a cocked position not in contact with the detonator.
 6. The apparatus of claim 1 wherein the means for packing off the well above the flow tool comprises: a string of tubular pipe of smaller diameter than the casing, extending into the well through the casing to a point adjacent the subsurface earth formation; means for sealing the annular space between the string of tubular pipe of smaller diameter and the casing to fluid flow positioned in the casing above the subsurface earth formation; and means for packing off the interior of the string of tubular pipe of smaller diameter connected to the wire line above the flow tool.
 7. The apparatus of claim 6 wherein the means for packing off tHe interior of the string of tubular pipe of smaller diameter comprises a zone isolating pack-off means which includes a hollow body portion having a through-bore through which the wire line may pass, locking means connected to the body portion for fixedly positioning the zone isolating pack-off means in the string of tubular pipe of smaller diameter, sealing means connected to the body portion for sealingly engaging the interior wall of the string of tubular pipe of smaller diameter, and a hollow throat section connected to the lower end of the body portion; wherein the upper portion of the housing of the flow tool comprises a neck having sealing means thereon whereby the neck may be drawn into sealing engagement with he throat section of the zone isolating pack-off means; and including means for releaseably connecting the zone isolating pack-off means to the wire line above the flow tool in spaced relationship with the flow tool; whereby the zone isolating pack-off means and the flow tool, while in spaced relationship, may be run into the well through the tubular pipe of smaller diameter to a point adjacent the subsurface earth formation at which point the locking means fixedly position the zone isolating pack-off means in the string of tubular pipe of smaller diameter, and whereby the zone isolating pack-off means may then be disconnected from the wire line thereby allowing the neck of the flow tool to be raised into sealing engagement with the throat section of the zone isolating pack-off means to pack off the interior of the string of tubular pipe of smaller diameter above the port section of the flow tool prior to cleaning the perforations.
 8. The apparatus of claim 7 including a seating nipple having a polished bore and one or more circular-internal grooves for receiving the locking means of the zone isolating pack-off means, the seating nipple being positioned in the string of tubular pipe of smaller diameter at a point adjacent the subsurface earth formation at which it is desired to pack off the interior of the string of tubular pipe of smaller diameter.
 9. The apparatus of claim 7 including means for reconnecting the zone isolating pack-off means to the wire line after cleaning the perforations.
 10. The apparatus of claim 9 wherein the means for releaseably connecting the zone isolating pack-off means to the wire line comprises at least one shear pin and wherein the means for reconnecting the zone isolating pack-off means to the wire line comprises at least two flexible arms operatively connected to the wire line and having upset ridges near the lower end thereof for lockingly engaging the zone isolating pack-off means.
 11. In a method of cleaning well perforations, in a well having a casing perforated adjacent a subsurface earth formation containing a fluid at a formation pressure, of the type wherein the perforated interval of the well bore is packed off with at least one packer to isolate the perforated interval of the well from fluids in the well above the perforated interval, and wherein a chamber of selected volume containing a gas at a pressure substantially lower than the formation pressure is then rapidly opened into fluid communication with the packed-off perforated interval to cause a selected volume of fluid to surge from the formation through the perforations into the casing carrying debris from the perforations into the well; the improvement which comprises, in a well having a relatively small diameter tubing extending into the casing to a point adjacent the perforated interval, the space between the casing and the tubing being closed above the perforated interval to fluid flow from the formation, the steps of: affixing to a wire line a flow tool comprising a chamber of selected volume closed at one end with a frangible disc and comprising a means for breaking the frangible disc; affixing to the wire line, above the flow tool, a means for packing off the tubing; lowering the flow tool and pack-off means into the tubing tO a point adjacent the perforated interval of the casing; packing off the tubing; activating the means for breaking the frangible disc to open the chamber into fluid communication with the perforated interval of the casing; and withdrawing the low tool and pack-off means from the well. 